Radiofrequency (RF) transmitters and receivers are found in a multiplicity of applications, particularly in the field of wireless communication and in the field of radar sensors. In the automotive sector, there is an increasing demand for radar sensors which can be used, inter alia, in driver assistance systems (advanced driver assistance systems, ADAS) such as adaptive cruise control (ACC or radar cruise control) systems, for example. Such systems are able to automatically adapt the speed of an automobile in order thus to maintain a safe distance from other automobiles driving ahead (and from other objects and pedestrians). Further applications in the automotive sector are, for example, blind spot detection, lane change assist and the like.
Modern radar systems use highly integrated RF circuits which can unify all core functions of an RF front end of a radar transceiver in a single housing (single chip radio transceiver). Such highly integrated RF circuits are usually referred to as monolithic microwave integrated circuits (MMICs). An RF front end typically (but not necessarily) contains, inter alia, a phase-control-loop-switched voltage-controlled oscillator (VCO), power amplifiers (PAs), directional couplers, mixers and associated control circuit arrangements for controlling and monitoring the RF front end. An MMIC may also comprise circuits for analog signal processing in the baseband (or in an intermediate frequency band) and analog-to-digital converters (ADCs) in order to facilitate digital signal processing. Depending on application, digitally controlled oscillators (DCOs) may also be used instead of VCOs.
Testing one or more RF circuit components is often desired or necessary in sensor applications in order to facilitate a fault-free operation of the sensors and observance of the desired measurement accuracy. For this reason, RF circuits used in radar sensors may comprise components that facilitate one or more tests/self-tests in order to test and/or characterize certain RF circuit components.